The present invention relates to limited slip and locking type differential gear mechanisms, and more particularly, to such differential gear mechanisms which include some sort of clutch arrangement for limiting or preventing (under certain, predetermined conditions) differentiation within the device.
As used herein, the term “differential gear mechanism” will be used to mean and include a device which is able to transmit torque from an input to one or more outputs, and in which there is a clutch assembly disposed between the input and the output, such that the amount of torque transmitted is a function of the extent of engagement of the clutch assembly. Within the scope of the present invention, the term “limited slip” will be used in regard to such differential gear mechanisms, and should be understood to mean and include both limited slip and locking differentials.
Although the axle retention arrangement of the present invention may be utilized with many different types and configurations of limited slip differential gear mechanisms, it is especially suited to, and necessary for, differential gear mechanisms of the type illustrated and described in U.S. Pat. No. 5,310,388, assigned to the assignee of the present invention and incorporated herein by reference. In the limited slip differential gear mechanism of the cited patent, there is a clutch pack operable to transmit torque between the input (ring gear and differential case) and the output (one of the side gears and its respective axle shaft), with the degree of engagement of the clutch pack being determined by the fluid pressure in a clutch piston chamber. The fluid pressure biases a clutch piston toward greater engagement of the clutch pack. The differential gear mechanism of the cited patent also includes a gerotor pump having one rotor fixed to rotate with the input and the other rotor fixed to rotate with the output (specifically, the axle shaft), such that the flow of pressurized fluid into the clutch piston chamber is generally proportional to the speed difference between the input and the output.
As is well known to those skilled in the differential art, each of the outputs (axle shafts) typically defines a set of external splines in splined engagement with a set of internal splines defined by the respective side gear of the differential gear set. In limited slip differential gear mechanisms of the type illustrated in the above-incorporated patent, the external splines of the axle shaft are also in splined engagement with the internal splines defined by the clutch coupling member (to which the inner clutch disks are splined), and are also in splined engagement with the inner rotor of the gerotor pump. The necessity of having the external splines of the axle shaft in splined engagement with three separate sets of internal splines makes it much more difficult to achieve the required axle retention, and in particular, to retain the axle shaft in such a way that, when necessary, the axle shaft can later be removed for service and maintenance.
In the differential gear mechanism of the above cited patent, it is not feasible to utilize a retention ring disposed about the axially inner end of the axle shaft, i.e., inboard of the side gear. In the subject embodiment of the present invention, there is no access to that portion of the differential gear mechanism through the conventional “window” in the case, because the member which serves as the “cover” for the outer differential housing is a structural member. Therefore, in order to get access to the location just inboard of the side gears, to insert or remove a retention ring, the entire axle assembly would have to be removed from the vehicle, to be able to remove the “cover”.
As is well known to those skilled in the art of differential assembly, installation of the externally splined axle shaft within the differential gear mechanism typically involves one or more steps in which the assembly operator rotates the axle shaft to achieve rotational alignment of the external splines with the mating internal splines of, for example, the respective side gear. If the axle shaft is to be retained within the differential gear mechanism by some sort of collapsible and expandable retention ring, the assembly operator will, at some point during the installation of the axle shaft, have to exert sufficient force on the axle shaft, in an axially inboard direction, to compress the retention ring, then move the axle shaft further axially inward to a position where the retention ring is then allowed to expand, and serve its function of retaining the axle shaft, i.e., to prevent movement axially in an outboard direction.
Typically, the process of rotating the axle shaft to achieve rotational alignment of the external and internal splines is done by the assembly operator, manually, whereas the step of applying sufficient axial force on the axle shaft to collapse the retention ring is achieved with the help of a piece of equipment such as a hydraulic or pneumatic cylinder. Thus, in those situations, it is not considered acceptable practice at the typical axle assembly plant for the differential manufacturer to provide an axle retention arrangement which requires rotation of the axle shaft (to align the splines) and, at the same time, pushing the axle shaft (axially, to collapse the retention ring).